Device and method for determining the firing angle

ABSTRACT

A device and a method are provided to, with the aid of a limiting module, advance the maximally retarded ignition angle by a value with respect to the static combustion limit. The timing advance of the maximally retarded ignition angle may be used to avoid uncontrolled combustions in the exhaust, so-called exhaust backfirings. Such exhaust backfirings may occur in dynamic operating states.

FIELD OF THE INVENTION

The present invention relates to a device and a method for determiningthe ignition angle of an internal combustion engine.

BACKGROUND INFORMATION

In the BOSCH Technical Information, Kombiniertes Zünd-undBenzineinspritzsystem MOTRONIC (Combined Ignition and Gasoline InjectionSystem MOTRONIC) (1987 722 011, KH/VDT-09.85-De), control units forelectronic ignition control are described, where between two ignitionprocesses, the control unit ascertains the optimal ignition angle fromengine information such as load, speed and temperature with reference toprogram maps. The ignition angle may thus be adapted individually tovarious operating states of the engine. The ignition angle may beadvanced or retarded by any value as desired as a function of switchingsignals.

The German Published Patent No. 196 51 238 describes an ignition controlsystem which contains a limiting module that limits the ignition angle,determined in light of engine information, to a maximally retardedvalue. Limitation of the ignition angle to a maximally retarded value isdesirable, since in response to the demand for a torque reduction or areduction in the thermal efficiency, the ignition angle may be retarded.However, the retarded ignition angle thus obtained may not exceed amaximally retarded value, since otherwise a permissible manifoldtemperature or a limiting value for emissions may be exceeded. Accordingto the related art, such a maximally retarded value, the so-calledstatic combustion limit (IASTAT(max)), may be determined in terms of thelimiting value for the emission of hydrocarbons and the limiting valuefor the manifold temperature.

During certain operating states of the engine, secondary reactions mayoccur in the exhaust, so-called backfirings, which are caused byunburned or partially burned fuel getting into the exhaust. Thebackfirings may lead to noise pollution and destruction of components.The static combustion limit lies at ignition angles which are tooretarded for the specific operating states.

SUMMARY OF THE INVENTION

A device and method, respectively, of the present invention may have theadvantage that, during specific operating states, by advancing themaximally retarded ignition angle, exhaust backfirings and thereforenoise pollution and destruction of components may be effectivelyavoided.

Advantageous further refinements and improvements of the device andmethod for determining the ignition angle are possible via exemplaryembodiments and/or exemplary methods of the present invention. Inparticular, an exemplary method may be used for operating states inwhich an engine dynamic exists, and there is no positive engagementbetween the engine and the drive train. It may be advantageous to shiftthe maximally retarded ignition angle in the advance direction withreference to a static combustion limit which is a function of a programmap, since this permits an even more targeted adaptation to engineparameters. It may also be advantageous to advance the ignition only ina specific period of time after determining the dynamic without positiveengagement, during which exhaust backfirings actually occur, in order toquickly make the entire ignition-angle range available again for anadjustment of the ignition angle. It likewise may prove to beadvantageous to observe a waiting time after detecting the dynamicwithout positive engagement, so that a maximum ignition-angle range maystill be made available over a longer period of time. For the samereason, it may be advantageous to cancel the ignition advance of themaximally retarded ignition angle immediately after detecting a positiveengagement between the engine and drive train. Since the occurrence ofexhaust backfirings is temperature-dependent, it may be advantageous tomake the amount of the ignition advance, as well as the waiting time andthe period of time in which the ignition advance is carried outtemperature-dependent. For the same reason, it may be advantageous totake the quantity of secondary air blown into the exhaust tract intoaccount for the amount of the ignition advance. This may be carried outwith a small expenditure of memory, since the quantity of secondary airis taken into consideration with the aid of a weighting factor.

Another operating state in which exhaust backfirings may be avoided by ashift of the maximally retarded ignition angle in the advance directionoccurs during the post-start. Here, a reduction in the emission ofhydrocarbons may be achieved by the advance of the maximally retardedignition angle, as well. It may prove to be advantageous to lead theadvance shift of the maximally retarded ignition angle during thepost-start slowly to the steady-state combustion limit, in order toprevent sudden torque changes. In the same way, it may advantageous tomake the period of time, in which the maximally retarded ignition angleis led to the steady-state combustion limit, a function of the enginetemperature and the quantity of secondary air blown into the exhausttract, since the leading may thus be carried out in a manner that it isadapted optimally to the engine parameters, and an unnecessary ignitionadvance is avoided. Given a selection of a linear leading-to function ofthe maximally retarded ignition angle, the computing expenditure may beadvantageously minimized. It may be also advantageous in the selectionof the advance of the maximally retarded ignition angle during thepost-start to take into account whether measures have been taken to heatthe catalytic converter, for because of the influencing of temperatureassociated with them, they may cause an increased occurrence ofbackfirings in the exhaust.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematically an exemplary device of the present inventionfor determining the ignition angle.

FIGS. 2 through 11 show schematically in flow charts, differentexemplary methods of the present invention for determining the ignitionangle.

DETAILED DESCRIPTION

FIG. 1 shows an exemplary device of the present invention fordetermining the ignition angle of an internal combustion engine. Theexemplary device for determining the ignition angle includes a controlunit 1 equipped with a memory and a processing unit. Control unit 1 alsocontains a limiting module 2 which limits an ignition angleIA(setpoint), determined in light of engine information, to a maximallyretarded value IA(max). The limiting is carried out in such a way thatwhen the ignition angle determined from engine information is smallerthan IA(max), then value IA(setpoint), and otherwise value IA(max) ispassed on to ignition system 3. The transfer of an ignition-angle valuefrom control unit 1 to ignition system 3 is shown in the drawing by aconnecting line and an arrow.

The exemplary device of the present invention for determining theignition angle also includes an element 4 for detecting dynamics, and anelement 5 for detecting a positive engagement between the engine and thedrive train. These elements may be integrated in control unit 1, but mayalso be located outside of control unit 1.

In addition, the exemplary device of the present invention includes anelement 6 for measuring the quantity of secondary air, an element 7 formeasuring load, an element 8 for measuring speed, an element 9 formeasuring time, an element 10 for measuring engine temperature and anelement 11 for determining catalytic-converter heating measures. Theelements having reference numerals 6 through 11 measure operatingparameters of an internal combustion engine and transmit valuescorresponding to the respective measured values to control unit 1. Thisis shown in FIG. 1 by connecting lines and arrows. Control unit 1processes the parameters in its processing unit and determines ignitionangle IA(setpoint) as a function of these parameters. This ignitionangle IA(setpoint), as described, thereupon passes through the limitingmodule. The limiting module may also be arranged outside of the controlunit.

Ignition system 3 contains electronics, one or more output stages,ignition coils, as well as one or more spark plugs. Control unit 1controls the ignition system in such a way that the spark plug or sparkplugs ignite at the ignition angle determined by control unit 1 andlimiting module 2.

If a specific engine-speed gradient is exceeded or a specific change inthe intake-manifold pressure per unit of time is exceeded, then element4 for detecting dynamics recognizes that the internal combustion engineis in a dynamic state. Element 4 for detecting dynamics then supplies afirst dynamics value JD. If the internal combustion engine is not in adynamic state, then the element for detecting dynamics supplies a seconddynamics value ND. This means that the so-called dynamics indicator haseither first dynamics value JD or second dynamics value ND. Both firstdynamics value JD and second dynamics value ND contain in each case adefinitively specified value. In this context, the speed, for example,is measured by element 8 for measuring speed, and the value is passed onto control unit 1. Control unit 1 determines from it the engine-speedgradient and supplies this value to element 4 for detecting dynamics.Analogously, the intake-manifold pressure is detected by a sensor, andthe change in the intake-manifold pressure is determined from it bycontrol unit 1.

The element for detecting positive engagement between the engine and thedrive train recognizes that there is no positive engagement when eitherthe clutch is depressed, or no gear is engaged. The clutch position andthe engaged gears are monitored by sensors located outside of controlunit 1. They supply their measured values to the control unit, theinformation then also being processed by the element for detectingpositive engagement. If no positive engagement exists between the engineand the drive train, then element 5 for detecting positive engagementsupplies a first positive-engagement value NK. Otherwise, element 5 fordetecting positive engagement supplies a second positive-engagementvalue JK. This means that the so-called positive-engagement indicatorhas either first positive-engagement value NK or secondpositive-engagement value JK. Both first positive-engagement value NKand second positive-engagement value JK contain in each case a fixed,predefined value.

Element 6 for measuring secondary air, with the aid of a flow-ratemeter, measures what quantity of secondary air is blown into the exhausttract. The measured value of the secondary-air quantity is passed on tocontrol unit 1. Element 7 for measuring load measures, in light of theintake-manifold pressure, what charge the cylinder has. Alternatively,the charge may be determined by a hot-film air-mass meter (HFM) or interms of the throttle-valve position. The element for measuring loadtransfers a load value, corresponding to the charge of the cylinder, tocontrol unit 1. Element 8 for measuring speed measures the speed of theinternal combustion engine, for example, in terms of the revolutions ofthe crankshaft, using an induction-type pulse generator or a Hall-effectsensor. The speed determined by element 8 for measuring speed is passedon to control unit 1. Element 9 for measuring time measures a time whichhas passed since the start of the engine or another specific point oftime. The time values measured by element 9 for measuring time arepassed on to control unit 1. Element 10 for measuring engine temperaturemeasures the temperature of the engine cooling water. These temperaturevalues are passed on to control unit 1.

Moreover, the exemplary device for determining the ignition anglecontains an element 11 which determines whether measures have been takento heat the catalytic converter. The catalytic converter may be heatedwhen the engine has only been running a short time, or, if the enginehas already been running, it has cooled off again. The element fordetermining the catalytic-converter heating measure passes on a firstcatalytic-converter heating value JH to control unit 1 when measureshave been taken to heat the catalytic converter, and otherwise passes ona second catalytic-converter heating value NH to control unit 1. Bothfirst catalytic-converter heating value JH and secondcatalytic-converter heating value NH contain in each case a fixed,predefined value. The elements of an internal combustion enginedesignated by reference numerals 4 through 11 continually ascertain thevalues to be passed on to the control unit, and also transmit thesevalues continually to the control unit. All the elements described inFIG. 1 are components of an exemplary device according to the presentinvention for determining the ignition angle in an internal combustionengine. The elements having reference numerals 4 through 11 may becombined in any way as desired, or else may be integrated into controlunit 1.

FIG. 2 describes an exemplary method of the present invention fordetermining the ignition angle of an internal combustion engine. In step13, the control unit checks whether a specific operating state, aso-called dynamic operating state (BS), has occurred. If such anoperating state has commenced, then maximally retarded ignition angleIA(max) is yielded from the sum of static combustion limit IASTAT(max)and a differential ignition angle DIA(max), which has a positive value.In this context, the ignition angle shifts in the advance direction arecounted positive, and the ignition angle shifts in the retard directionare counted negative. Thus, the maximally retarded ignition angle, withrespect to static combustion limit IASTAT(max), is advanced by the valueof differential ignition angle DIA(max). This calculation of maximallyretarded ignition angle IA(max) is carried out in step 15. If a dynamicoperating state BS has not commenced, then the exemplary method jumps tostep 20, in which maximally retarded ignition angle IA(max) is yieldedfrom static combustion limit IASTAT(max). If the maximally retardedignition angle is ascertained according to step 15 or 20, thiscalculation being carried out by control unit 1, then the calculatedvalue of maximally retarded ignition angle IA(max) is passed on tolimiting module 2. The exemplary method thereupon jumps back again tostep 13. Static combustion limit IASTAT(max) may be read out from thememory of control unit 1 from a load- and speed-dependent program map.The load and the speed of the engine are measured by elements 7 and 8,respectively.

FIG. 3 shows a further exemplary embodiment of a exemplary methodaccording to the present invention. The exemplary method first passesthrough step 21, in which the control unit queries the value supplied tothe control unit by element 4 for detecting dynamics. If element 4 fordetecting dynamics supplies a first dynamics value JD to the controlunit, then in the next step 25, element 5 for detecting positiveengagement between the engine and drive train is queried for thecorresponding value. If first positive-engagement value NK is applied tothe control unit, then the exemplary method is continued with step 15.Analogous to FIG. 2, step 15 contains a timing advance of the maximumignition angle by the amount of a differential ignition angle. Here, thecorresponding differential ignition angle bears the designation firstdifferential ignition angle DIA1(max). If element 4 for detectingdynamics supplies second dynamics value ND to control unit 1, then theexemplary method is continued with step 20. If element 5 for detecting apositive engagement between engine and drive train supplies secondpositive-engagement value JK to the control unit, then the exemplarymethod is likewise continued with step 20. In the same way as in FIG. 2,step 20 includes that the maximally retarded ignition angle results fromstatic combustion limit IASTAT(max). As up till now, in the furtherdescription of the exemplary embodiments, identical reference numeralsdenote identical method steps. After a calculation of maximally retardedignition angle IA(max) either with the aid of step 15 or using step 20,the exemplary method jumps again to step 21.

The conditions formulated in step 21 and in step 25 yield a firstdynamic operating state BD1. It is characterized in that the internalcombustion engine is in a dynamic state, and at the same time, nopositive engagement exists between the engine and drive train. Such anoperating state may be illustrated in terms of a revving-up. Such arevving-up is caused, for example, by quickly depressing the acceleratorand thereupon quickly releasing it again. During the release of theaccelerator, the control unit receives the demand to reduce torque. Ingeneral, this is done via the ignition angle. The torque may be reducedvia the ignition angle in such a way that the ignition angle is shiftedin the retard direction. In general, this timing retard of the ignitionangle reaches up to the maximally retarded ignition angle. Due to thechange in pressure, which occurs suddenly in response to revving-up,injected, but not yet vaporized fuel, which is present in the intaketract as wall film, is sucked into the combustion chamber in which toorich a mixture is then present. Given an ignition angle corresponding tothe static combustion limit, this mixture cannot be completely burned.Therefore, islands of unburned or partially burned mixture get into theexhaust tract. Because of the high temperatures prevailing in theexhaust tract, self-ignition of these unburned or partially burnedislands may occur. The reactions may be intensified by the blowing in ofsecondary air. The secondary reactions in the exhaust tract are known asexhaust backfirings or backfirings. These exhaust backfirings may beavoided if the maximally retarded ignition angle does not correspond tothe static combustion limit, but rather is shifted to more advancedignition angles. Then, even given too rich a mixture, the combustion iscarried out completely, and no unburned or partially burned mixture ispresent any longer in the exhaust. Thus, as described in step 15, inresponse to revving-up, i.e. given the presence of dynamics withoutpositive engagement between engine and drive train, maximally retardedignition angle IA(max) may be required to be shifted in the advancedirection by the amount of a first differential ignition angleDIA1(max). In this context, first differential ignition angle DIA1(max)may be selected as a function of temperature. For example, DIA1(max) maybe stored in a temperature-dependent characteristic curve in a memory.Such a temperature dependence of first differential ignition angleDIA1(max) may be advantageous because the combustion, that is to say,the completeness of the combustion, is influenced by the enginetemperature. The temperature of the intake air is measured by element 10for determining temperature.

FIG. 4 shows a further exemplary embodiment of an exemplary method fordetermining the ignition angle. Steps 21, 25 and 20 correspond to thesteps having the same reference numerals in FIG. 3, and therefore arenot described again separately. If element 5 for detecting a positiveengagement between engine and drive train detects that no positiveengagement exists, then the exemplary method passes through a new step28 in which it is checked whether the exemplary method has alreadyexceeded a so-called occur time t(occur) since determining a firstdynamic operating state BD1. If this is not the case, then the exemplarymethod arrives at step 15, which again corresponds to step 15 in FIG. 3.If occur time t(occur) has been exceeded, then the exemplary methodarrives at step 21. Achieved by the new step 28 is that, before a newcheck of the operating state of the engine is carried out, initiallywithin a specific period of time, occur time t(occur), the ignitionangle is shifted in the advance direction. It has turned out that,within this applicable occur time t(occur), exhaust backfirings occurwith increasing frequency, so that a timing advance of the maximallyretarded ignition angle within occur time t(occur) is useful. This occurtime t(occur) may be contained in the control unit in atemperature-dependent characteristic curve. This may be advantageous,since the combustion, and therefore also the length of the period oftime in which exhaust backfirings occur, is a function of the enginetemperature.

The further exemplary embodiment of the exemplary method according tothe present invention shown in FIG. 5 contains the same steps as theexemplary embodiment shown in FIG. 4. Therefore, the individual stepsare not explained once again. The exemplary method shown in FIG. 5differs from the exemplary method shown in FIG. 4 in that, aftermaximally retarded ignition angle IA(max) has been calculated in step15, and occur time t(occur) is not yet exceeded (step 28), it is checkedonce more whether a positive engagement between engine and drive trainexists in step 25. If this is the case, then the exemplary method jumpsimmediately to step 20, in which the maximally retarded ignition angleresults from static combustion limit IASTAT(max). With the aid of theexemplary method according to the present invention shown in FIG. 5, itis possible to react immediately if a positive engagement exists betweenengine and drive train. This may be advantageous, since in response to apositive engagement, which, for example, may be triggered by engagingthe clutch, vibrations occur in the drive train which may requirecorrection by interventions in the ignition angle. To that end, thepresence of a maximum ignition-angle range, which extends up to staticcombustion limit IASTAT(max), is desirable. In this context, exhaustbackfirings possibly occurring for a brief period after the engagementof the clutch may be tolerated. Since, however, the engine isdecelerated by the process of engaging the clutch, the dynamics of theengine are reduced such that secondary reactions in the exhaust causedby the dynamics are removed very quickly.

FIG. 6 shows another exemplary embodiment of the exemplary methodaccording to the present invention for determining the ignition angle ofan internal combustion engine. It differs from the exemplary methodpresented in FIG. 5, in that a step 30 is inserted which is carried outafter step 21. This step 30 includes the waiting of a waiting timet(reac) after element 4 for detecting dynamics has detected a dynamic instep 21. This waiting time t(reac) is observed before, in step 25,element 5 for detecting positive engagement between engine and drivetrain checks whether or not a positive engagement exists between theengine and drive train. The implementation of such a step 30, in which awaiting time t(reac) is observed, may be advantageous, since secondaryreactions in the exhaust only occur after this waiting time t(reac).This time t(reac) is applicable. Furthermore, waiting time t(reac) maybe available in a temperature-dependent characteristic curve in controlunit 1. This is because, as already presented in the clarification ofthe previous exemplary embodiments, the combustion, and therefore alsothe period of time for the occurrence of exhaust backfirings, is afunction of the engine temperature.

FIG. 7 shows a further exemplary embodiment of a exemplary methodaccording to the present invention for determining the ignition angle ofan internal combustion engine. This exemplary method differs from theexemplary method presented in FIG. 6 in terms of the additionallyinserted steps 35 and 40 Therefore, the remaining steps are notexplained again. If, in step 28, the query after elapsed occur timet(occur) reveals that the time after detecting the dynamics is less thanoccur time t(occur), then the exemplary method jumps to step 35, inwhich the control unit queries the value of the secondary-air quantitytransmitted by the element for measuring secondary air. If this value isgreater than a first limiting value LG1, then the exemplary method jumpsto step 40. In this step 40, maximally retarded ignition angle IA(max)is calculated as the sum of static combustion limit IASTAT(max) and asecond differential ignition angle DIA2(max). If the quantity ofsecondary air in step 35 has not exceeded first limiting value LG1, thenthe exemplary method jumps to step 15, in which, as already in theexemplary methods of the present invention presented in FIGS. 2 through6, the maximally retarded ignition angle is calculated as the sum of afirst differential ignition angle DIA1(max) and static combustion limitIASTAT(max). After passing step 15 or step 40, the exemplary methodjumps back to step 28.

The quantity of secondary air blown into the exhaust tract influencesthe igniting of the islands of unburned or partially burned fuel. Thus,the quantity of secondary air blown into the exhaust tract influencesthe development of exhaust backfirings. If the quantity of secondary airblown in exceeds a critical value, exhaust backfirings may occur withincreased frequency. Therefore, here a further timing advance of themaximally retarded ignition angle with respect to static combustionlimit IASTAT(max) is desirable. Accordingly, upon exceeding a specificquantity of secondary air blown in, another second differential ignitionangle DIA2(max) may need to be taken into account. This operating stateis also designated as second dynamic operating state BD2. Seconddifferential ignition angle DIA2(max) may also be obtained from firstdifferential ignition angle DIA1(max) by multiplication with a firstweighting factor F1. This factor requires a value greater than 1. Seconddifferential ignition angle DIA2(max) and first weighting factor F1,respectively, may in turn be set in the application. Analogous toDIA1(max), second differential ignition angle DIA2(max) and the firstweighting factor, respectively, may be contained in control unit 1 in atemperature-dependent characteristic curve. It is also possible for aplurality of first limiting values to exist for the quantity ofsecondary air blown in. New second differential ignition anglesDIA2(max) and first weighting factors F1, respectively, may be stored inthe control unit for each first limiting value.

FIG. 8 shows a further exemplary embodiment of the exemplary methodaccording to the present invention for determining the ignition angle.In step 45, it is queried whether the value, provided to the controlunit by the element for measuring time, has exceeded a time value, starttime t(start). If this is not the case, then there is a wait for aspecific time, and step 45 is again carried out with the time query. Ifa start time t(start) is exceeded, then the exemplary method jumps tostep 50, in which the maximally retarded ignition angle is yielded asthe sum of a third differential ignition angle DIA3(max) and staticcombustion limit IASTAT(max). The exemplary method thereupon jumps tostep 55, in which the control unit queries the value provided by theelement for measuring time. If a post-start time t(poststart) is notexceeded, then the exemplary method jumps once more to step 50. If thispost-start time t(poststart) is exceeded, then the exemplary method iscontinued, in general in that the maximally retarded ignition angle isyielded from the static combustion limit. One of the exemplary methodsdescribed in FIGS. 2 through 7 may also follow. This dynamic operatingstate, in which a third differential ignition angle DIA3(max) yields atiming advance of the maximally retarded ignition angle with respect tothe static combustion limit, is designated as third dynamic operatingstate BD3. This operating state is achieved within a period of timebetween start time t(start) and post-start time t(poststart), theso-called post-start phase. An occurrence of exhaust backfirings and anintensified emission of hydrocarbons, which develop due to the unburnedor partially burned mixture getting into the exhaust, has been measuredfor this operating state, as well. Therefore, a timing advance of themaximally retarded ignition angle with respect to static combustionlimit IASTAT(max) may also be advantageous here. Prior to start timet(start), the maximally retarded ignition angle assumes a maximallyretarded start-time ignition angle IAS(max) which lies at more advancedignition angles with respect to IASTAT(max).

FIG. 9 shows another exemplary embodiment for a exemplary methodaccording to the present invention. This exemplary method is analogousto the exemplary method described in FIG. 8, but additionally includesstep 60. After the maximally retarded ignition angle has been calculatedas the sum of third differential ignition angle DIA3(max) and staticcombustion limit IASTAT(max) in step 50, the exemplary method reachesstep 60. In this step 60, a time meter t is increased by a first timestep t(step1). This first time step t(step1) was initialized at thepoint of time when step 50 was passed through for the first time. Afterthe time meter has been increased by a first time step t(step1) in step60, the exemplary method reaches step 55.

In the exemplary method of the present invention shown in FIG. 9, thirddifferential ignition angle DIA3(max) is calculated as function Fc oftime meter t in control unit 1. Since the time meter is increased by afirst time step t(step1) with each pass-through of the loop,differential ignition angle DIA3(max) changes in response to eachpass-through of the loop. In this context, the loop is made of steps 50,60 and 55. Function Fc, stored in control unit 1, for third differentialignition angle DIA3(max) is a monotonically decreasing function Fc ofthe time meter. The value range of function Fc(t) may lie between thevalues 0 and the difference between maximally retarded start-timeignition angle IAS(max) and static combustion limit IASTAT(max). Thus,it is possible to shift the maximally retarded ignition angle, whichresults as the sum of third differential ignition angle DIA3 as functionof t, and static combustion limit IASTAT(max), slowly to more retardedignition angles, until maximally retarded ignition angle IA(max) hasreached the value of static combustion limit IASTAT(max). This may beadvantageous, since sudden changes in torque are thereby avoided. Inthis context, it is possible to establish first time step t (step1) incontrol unit 1 as a function of the temperature. This may beadvantageous, since the size of first time step t (step1) determines thelength of the post-start phase. If the engine temperature is high, thenexhaust backfirings and stronger hydrocarbon emissions, respectively,occur only in a smaller period of time after ending the start phase.Thus, the post-start phase may be made shorter with a greater value forthe first time step. However, if the engine temperature is low, thenexhaust backfirings and hydrocarbon emissions occur within a longerperiod of time after ending the start phase. Consequently, the value ofthe first time step may then need to be selected to be smaller.Furthermore, monotonically decreasing function Fc may represent a linearfunction of the time meter. This may be advantageous, since thecomputing time in the control unit is minimized by the simple formationof function Fc.

FIG. 10 shows a further exemplary embodiment of the exemplary methodaccording to the present invention for determining the most retardedignition angle. The exemplary method differs from the exemplary methodpresented in FIG. 9 by the additional insertion of exemplary methodsteps 65, 70 and 75. After the maximally retarded ignition angle hasbeen calculated in step 50 as the sum of a third differential ignitionangle DIA3(max) and the static combustion limit, the exemplary methodreaches step 65. In this step 65, the value which element 6 formeasuring the secondary air provides to the control unit is queried.This value contains the quantity of secondary air blown into the exhausttract. If the quantity of secondary air measured in step 65 is less thana second limiting value LG2, then the exemplary method arrives at step70, in which the value 1 is assigned to a second weighting factor F2. Ifthe quantity of secondary air blown in is greater than second limitingvalue LG2, then the exemplary method arrives at step 75. In this step75, second weighting factor F2 is assigned a value smaller than 1 incontrol unit 1. The value of first time step t (step1) is multiplied bythis second weighting factor F2, which was determined either in step 75or in step 70, the product being designated by second time stept(step2), before time meter 1 is now increased by second time step t(step2) in step 60. Realized in the exemplary method of the presentinvention shown in FIG. 10 is that when a specific value of asecondary-air quantity LG2 is exceeded, the shift of the ignition anglein the advance direction in the post-start is carried out over a longerperiod of time. This lengthening of the post-start phase may beadvantageous, since if a specific secondary-air quantity is exceeded,exhaust backfirings may occur with increasing frequency.

FIG. 11 shows a further exemplary embodiment of a exemplary methodaccording to the present invention. The exemplary embodiment in FIG. 11differs from the exemplary embodiment shown in FIG. 8 by the insertionof steps 80 and 85. As described in the explanations with respect toFIG. 8, after a start time t(start) has been exceeded (step 45), theexemplary method arrives at step 80 in which it is asked whether element11 for determining catalytic-converter heating measures has supplied afirst catalytic-converter heating value JH or a secondcatalytic-converter heating value NH to control unit 1. This means, itis asked whether or not the catalytic converter is heated. If element 11has supplied second catalytic-converter heating value NH to control unit1, i.e. when no catalytic converter heating is carried out, then theexemplary method reaches step 50 in which the maximally retardedignition angle is formed as the sum of third differential ignition angleDIA3(max) and the static combustion limit. The exemplary method isthereupon continued as was described with reference to FIG. 8. If instep 80, element 11 for determining catalytic-converter heating measuressupplies first catalytic-converter heating value JH to control unit 1,i.e. catalytic converter heating is carried out, then the exemplarymethod reaches step 85 in which the maximally retarded ignition angle isformed as the sum of a fourth differential ignition angle DIA4(max) andthe static combustion limit. The so-called fourth dynamic operatingstate BD4 has then commenced. Thereupon, the exemplary method continuesanalogous to the exemplary method described in FIG. 8. Therefore, if thecatalytic converter is being heated, a fourth differential ignitionangle (DIA4(max)), different than without catalytic-converter heating,is taken into account for the maximally retarded ignition angle. Thismay be advantageous, since the occurrence of exhaust backfirings is afunction of temperature, and with the implementation ofcatalytic-converter heating measures, the temperature in the exhausttract is changed.

Analogous to third dynamic operating state BD3, as presented in FIGS. 9and 10, for fourth dynamic operating state BD4, a time-dependent changeof fourth differential ignition angle DIA4(max), which may berepresented in a linear function of the time, may be carried out. Thevalues of fourth differential ignition angle DIA4(max), analogous toDIA3(max), may lie in a range between zero and the difference betweenmaximally retarded start-time ignition angle IAS(max) and staticcombustion limit IASTAT(max). In this context, the width of first timestep t(step1) may likewise be made a function of the temperature. In thesame way, for the width of the time step for the time-dependence offourth differential ignition angle DIA4(max), the quantity of secondaryair blown in may be taken into account analogous to the time-step-widthdependence of third differential ignition angle DIA3(max).

What is claimed is:
 1. A device for determining an ignition angle of aninternal combustion engine, comprising: a limiting module configured tolimit a setpoint ignition angle to a maximally retarded ignition anglefor an operation of the engine, the setpoint ignition angle optimized asa function of operating parameters of the engine; and a control unitcontaining functions to differentiate between a steady operating stateand at least one dynamic operating state, wherein in the steadyoperating state, the maximally retarded ignition angle assumes a valueof a static combustion limit; and wherein for each dynamic operatingstate, the control unit contains at least one differential ignitionangle which, upon occurrence of a respective dynamic operating state, isconfigured to bring about a shift of the maximally retarded ignitionangle to more advanced ignition angles with respect to the staticcombustion limit.
 2. The device of claim 1, wherein the value of thestatic combustion limit is obtainable from at least one of aspeed-dependent and a load-dependent program map stored in the controlunit.
 3. The device of claim 1, wherein the maximally retarded ignitionangle is an absolute angle.
 4. A device for determining an ignitionangle of an internal combustion engine, comprising: a limiting moduleconfigured to limit a setpoint ignition angle to a maximally retardedignition angle for an operation of the engine, the setpoint ignitionangle optimized as a function of operating parameters of the engine; anda control unit containing functions to differentiate between a steadyoperating state and at least one dynamic operating state, wherein in thesteady operating state, the maximally retarded ignition angle assumes avalue of a static combustion limit; and wherein for each dynamicoperating state, the control unit contains at least one differentialignition angle which, upon occurrence of a respective dynamic operatingstate, is configured to bring about a shift of the maximally retardedignition angle to more advanced ignition angles with respect to thestatic combustion limit; a dynamics indicator configured to detect adynamic, the dynamics indicator exhibiting a first dynamics value inresponse to detecting an existing dynamic and otherwise exhibiting asecond dynamics value; and a positive-engagement indicator configured todetect a positive engagement between the engine and a drive train, thepositive-engagement indicator exhibiting a second positive-engagementvalue in response to detecting an existing positive engagement andotherwise a first positive-engagement value, wherein a first dynamicoperating state results when the dynamics indicator exhibits the firstdynamics value and the positive-engagement indicator exhibits the firstpositive-engagement value, at least one first differential ignitionangle being present in the control unit for the first dynamic operatingstate.
 5. The device of claim 4, wherein the maximally retarded ignitionangle is shifted during an occur time.
 6. The device of claim 5, whereinthe maximally retarded ignition angle is shifted after a waiting timehas elapsed after detecting the first dynamic operating state.
 7. Thedevice of claim 4, wherein the control unit provides a switchingfunction configured to make a switch back into the steady operatingstate immediately after the positive-engagement indicator exhibits thesecond positive-engagement value.
 8. The device of claim 4, wherein thecontrol unit contains values of the at least one first differentialignition angle in a temperature-dependent characteristic curve.
 9. Thedevice of claim 6, wherein the control unit contains values of at leastone of the waiting time and the occur time in a temperature-dependentcharacteristic curve.
 10. The device of claim 6, wherein at least onevalue of the waiting time and at least one value of the occur time areset in an application.
 11. The device of claim 4, further comprising: anelement for measuring a quantity of secondary air present; wherein asecond dynamic operating state results when the dynamics indicatorexhibits the first dynamics value and the positive-engagement indicatorexhibits the first positive-engagement value and the quantity ofsecondary air exceeds a first limiting value, at least one seconddifferential ignition angle being present in the control unit, as afunction of the first limiting value, for the second dynamic operatingstate.
 12. The device of claim 11, wherein at least one value of thesecond differential ignition angle for the second dynamic operatingstate is derived from at least one value of the first differentialignition angle by multiplication with a first weighting factor, thefirst weighting factor being a function of the first limiting value. 13.A device for determining an ignition angle of an internal combustionengine, comprising: a limiting module configured to limit a setpointignition angle to a maximally retarded ignition angle for an operationof the engine, the setpoint ignition angle optimized as a function ofoperating parameters of the engine; a control unit containing functionsto differentiate between a steady operating state and at least onedynamic operating state, wherein in the steady operating state, themaximally retarded ignition angle assumes a value of a static combustionlimit; and wherein for each dynamic operating state, the control unitcontains at least one differential ignition angle which, upon occurrenceof a respective dynamic operating state, is configured to bring about ashift of the maximally retarded ignition angle to more advanced ignitionangles with respect to the static combustion limit; and an element toperform a time measurement; wherein a first dynamic operating stateresults when a start time is exceeded and a post-start time falls shortof a defined value, a processing unit of the control unit supplying atleast one first differential ignition angle for the first dynamicoperating state.
 14. The device of claim 13, further comprising: anelement for monitoring whether measures have been taken to heat acatalytic converter; wherein a second dynamic operating state resultswhen the start time is exceeded and the post-start time falls short ofthe defined value and the catalytic converter is heated, the processingunit of the control unit supplying at least one second differentialignition angle for the second dynamic operating state.
 15. The device ofclaim 14, wherein at least one value of at least one of the firstdifferential ignition angle and the second differential ignition angleis time-dependent, the processing unit of the control unit supplying oneof a new first differential ignition angle value and a new seconddifferential ignition angle value after each first time step.
 16. Thedevice of claim 15, wherein a size of the first time step is a functionof temperature.
 17. The device of claim 15, wherein: the control unitcontains an element for measuring a quantity of secondary air present,the control unit providing a characteristic curve which contains atleast one second weighting factor as a function of the quantity ofsecondary air present, and the control unit recalculating a time stepwhen a second limiting value of the secondary-air quantity is exceeded,wherein a second time step results as a product of the second weightingfactor and the first time step.
 18. The device of claim 15, wherein atleast one value of at least one of the first differential ignition angleand the second differential ignition angle includes a value ranging from0 to a difference between a maximally retarded start-time ignition angleand the static combustion limit, the maximally retarded start-timeignition angle representing the maximally retarded ignition angle fortimes smaller than the start time.
 19. The device of claim 18, whereinthe control unit calculates the at least one value of the at least oneof the first differential ignition angle and the second differentialignition angle in terms of a monotonically decreasing function as afunction of one of the first time step and the second time step.
 20. Thedevice as recited in claim 19, wherein a linear function of one of thefirst time step and the second time step is present in a memory of thecontrol unit as the monotonically decreasing function.
 21. A method fordetermining an ignition angle of an internal combustion engine with acontrol unit and a limiting module, comprising: optimizing a setpointignition angle as a function of operating parameters of the engine;limiting the setpoint ignition angle to a maximally retarded ignitionangle for an operation of the engine; making a differentiation in thecontrol unit between a steady operating state and at least one dynamicoperating state, wherein in the steady operating state, the maximallyretarded ignition angle assumes a value of a static combustion limit;calculating at least one differential ignition angle for each dynamicoperating state; and shifting, upon occurrence of a respective dynamicoperating state, the maximally retarded ignition angle by the at leastone differential ignition angle to more advanced ignition angles withrespect to the static combustion limit.
 22. The method of claim 21,wherein the calculating step further includes storing the at least onedifferential ignition angle.
 23. The method of claim 21, furthercomprising the step of: ascertaining the value of the static combustionlimit from at least one of a speed-dependent and a load-dependentprogram map.
 24. The method of claim 23, wherein the maximally retardedignition angle is an absolute angle.
 25. A method for determining anignition angle of an internal combustion engine with a control unit anda limiting module, comprising: optimizing a setpoint ignition angle as afunction of operating parameters of the engine; limiting the setpointignition angle to a maximally retarded ignition angle for an operationof the engine; making a differentiation in the control unit between asteady operating state and at least one dynamic operating state whereinin the steady operating state, the maximally retarded ignition angleassumes a value of a static combustion limit; calculating at least onedifferential ignition angle for each dynamic operating state, andshifting, upon occurrence of a respective dynamic operating state, themaximally retarded ignition angle by the at least one differentialignition angle to more advanced ignition angles with respect to thestatic combustion limit; wherein a dynamics indicator exhibits a firstdynamics value in response to an existing dynamic, and otherwiseexhibits a second dynamics value, and wherein a positive-engagementindicator exhibits a second positive-engagement value in response to anexisting positive engagement between engine and drive train, andotherwise exhibits a first positive-engagement value, so that a firstdynamic operating state results when the dynamics indicator exhibits thefirst dynamics value and the positive-engagement indicator exhibits thefirst positive-engagement value, at least one first differentialignition angle being at least one of determined and stored in thecontrol unit for the first dynamic operating state.
 26. The method ofclaim 25, wherein the at least one first differential ignition angle isactivated during an occur time.
 27. The method of claim 25, wherein theat least one first differential ignition angle is activated after awaiting time has elapsed after detecting the first dynamic operatingstate.
 28. The method of claim 25, wherein immediately after thepositive-engagement indicator exhibits the second positive-engagementvalue, operating state switches back into the steady operating state.29. The method of claim 25, wherein values of the at least one firstdifferential ignition angle are taken from a temperature-dependentcharacteristic curve.
 30. The method of claim 26, wherein values of theoccur time are taken from a temperature-dependent characteristic curve.31. The method of claim 27, wherein values of the waiting time are takenfrom a temperature-dependent characteristic curve.
 32. The method ofclaim 26, wherein values of the occur time are set in an application.33. The method of claim 27, wherein values of the waiting time are setin an application.
 34. The method of claim 25, further comprising thestep of: measuring a quantity of secondary air present; wherein a seconddynamic operating state results when the dynamics indicator exhibits thefirst dynamics value and the positive-engagement indicator exhibits thefirst positive-engagement value and the quantity of secondary airpresent exceeds a first limiting value, at least one second differentialignition angle being at least one of calculated and stored in thecontrol unit for the second dynamic operating state as a function of thefirst limiting value.
 35. The method of claim 34, wherein values of theat least one second differential ignition angle are calculated for thesecond dynamic operating state by multiplying at least one value of thefirst differential ignition angle by a first weighting factor, the firstweighting factor being a function of the first limiting value.
 36. Amethod for determining an ignition angle of an internal combustionengine with a control unit and a limiting module, comprising: optimizinga setpoint ignition angle as a function of operating parameters of theengine; limiting the setpoint ignition angle to a maximally retardedignition angle for an operation of the engine; making a differentiationin the control unit between a steady operating state and at least onedynamic operating state wherein in the steady operating state, themaximally retarded ignition angle assumes a value of a static combustionlimit; calculating at least one differential ignition angle for eachdynamic operating state; shifting, upon occurrence of a respectivedynamic operating state the maximally retarded ignition angle by the atleast one differential ignition angle to more advanced ignition angleswith respect to the static combustion limit; and performing a timemeasurement, so that a first dynamic operating state results when astart time is exceeded and a post-start time falls short of a definedvalue, at least one first differential ignition angle being at least oneof stored and calculated for the first dynamic operating state.
 37. Themethod of claim 36, further comprising the step of: monitoring whetherthe catalytic converter is being heated; wherein a second dynamicoperating state results when the start time is exceeded and thepost-start time falls short of the defined value and measures have beentaken to heat the catalytic converter, at least one second differentialignition angle being at least one of stored and calculated for thesecond dynamic operating state.
 38. The method of claim 37, wherein atleast one of the first differential ignition angle and the seconddifferential ignition angle is time-dependent, at least one of a newfirst differential ignition angle value and a new second differentialignition angle value being calculated after each first time step. 39.The method of claim 38, wherein a size of the first time step is afunction of temperature.
 40. The method of claim 38, further comprisingthe steps of: measuring a quantity of secondary air present; andproviding a characteristic curve which contains at least one weightingfactor as a function of the quantity of secondary-air present, a secondtime step being calculated by multiplying the first time step by theweighting factor when a limiting value of the quantity of secondary airpresent is exceeded.
 41. The method of claim 38, wherein at least onevalue of at least one of the first differential ignition angle and thesecond differential ignition angle includes angles of a value rangingfrom 0 to a difference between a maximally retarded start-time ignitionangle and the static combustion limit, the maximally retarded start-timeignition angle representing a most retarded, maximum ignition angle fortimes smaller than the start time.
 42. The method of claim 41, whereinthe at least one value of the at least one of the first differentialignition angle and the second differential ignition angle is calculatedin terms of a monotonically decreasing function as a function of atleast of one of the first time step and the second time step.
 43. Themethod of claim 42, wherein the monotonically decreasing functionrepresents a linear function of at least one of the first time step andthe second time step.